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TIT~E OF THE INV~TTON:
ELECTROPHOTOGRAPHIC MAGNETIC CARRIER AND PROCESS FOR
PRODUCING THE SAME
BACK~OUND OF TH~ I~VENTION:
The present invention relates to an electrophotographic
~agnetic carrier and a process for producing the magnetic
carrier, and more particularly, to an electrophotographic
magnetic carrier not only having a high saturation
magnetization and a freely controllable charge amount, but
also being free ~rom falling-of~ or separation of magnetic
fine particles from a core particle, for example, in case
where a granulated particle comprising the magnetic ~ine
particles is used as a core particle.
AS iS we~1 known in the conventional
e~ectrophotographic processes, there has been adopted an
image-developing method comprising using a photosensitive
conductor formed of a photoconductive material such as
selenium, OPC (organic photo-semiconductor) or amorphous
si~icone, forming an electrostatic latent image on the
photosensitive conductor by various methods and
electrostatically attaching to the latent image a toner
charged to a polarity reverse to that of the latent image.
In such an image-developing method, there have been
used particles called a carrier' which is brought into
frictional contact with a toner to impart an adequate amount
of positive or negative charge to the toner. The thus
charged toner is transported t.hrough a developing sleeve
usin~ a magnetic force exerted by a magnet accom~odated in
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the developing sleeve~ to a deve~oping zone adjacent to a
surface of the photosensitive conductor where the latent
~mage is formed.
In recent years, the electrophotographic techniques
have been widely applied to copying ~ach;nes, printers or
the like. In these applications, it has been required to
accurately reproduce fine lines, small characters,
photographs, color images or the like. Further, it have
also been required to achieve a high-~uality or high-grade
image, a high-speed or continuous operation or the like.
These de~ands are expected to be more and more increased in
the future.
As conventional carriers, there have been used magnetic
particles such as iron powder (a mechanically crushed iron
powder, an electrolytic iron powder, a reduced iron powder,
a heat-treated iron powder, a sintered iron powder or the
like), ferrite particles ~Mn ferrite particles, Li-Mn
ferrite particles, Ni-Zn ferrite particles, Mn-Zn ferrite
particles, Cu-Zn ferrite particles or the like) or magnetite
particles or the like. However, any of these particles
exert a large stress against toner due to an impact force
therebetween when both are mixed and agitated together in a
developing device, so that the developer suffers from
aeterioration in its durability during a long-term use.
In addition, irregularities on surfaces of magnetic
particles causes the same problem concerning the durabilitY
of de~eloper as mentioned above, especially when toner is
deposited into concave portions thereof.
Further, in some methods of producing magnetic
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particles, there arises such an disadvantage that a large
amount of fine particles having as small a diameter as not
more than 1 ~m are present therein. The fine particles tend
to be fallen-off or separated from the surface of the
magnetic particle which , for example, comprises magnetic
fine particles, thereby causing such a problem that when the
magnetic particles are mixed with a colored toner, the color
tone of the toner is deteriorated. Especially, in the case
of yellow-colored toner, the above-mentioned problem becomes
more remarkable.
In order to solve these problems, there have been
proposed resin-coated magnetic particles obtained by coating
as a core particle a magnetic particle of a granulated
particle comprising magnetic fine particles or iron powder
(iron particle) with an insulating resin as a carrier.
However, in the case where the granulated particle
comprising the magnetic fine particles is coated with a
resin in a large thickness to inhibit falling-off or
separation of magnetic fine particles from the core particle,
the volume resistivity of the carrier itself becomes too
large, thereby causing such a problem that images having a
deteriorated quality are produced, e.g., images showing too
sharp edges or conversely solid images having too low toner
density.
Further, when the core particle is coated with a resin,
irregularities on the surface of each core particle are
reflected on the surface of resin layer formed thereon, so
that there is caused a so-called "spent'l phenom~non that
toner is deposited into concave portions thereof during a
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long-term operation. Thus, in the case of the resin-coated
magnetic particles, the problem concerning-the durability of
developer still r~m~; n~ unsolved. Furthermore, the
conventional resin~coated magnetic particles are
deteriorated in adhesion between the core particle and the
coating resin, thereby causing such a problem that the
resin-coating layer is peeled-off or separated from the core
particle during a long-tenm use.
In order to solve the former problem concerning the
high volume resistivity, in Japanese Patent Applications
Laid-open (KOKAI) Nos. 2-120750(1990) and 3-72372(1991), it
has been proposed to incorporate a conductive material such
as carbon black or metal oxides into the resin-coating layer.
However, there still exist problems that the content of the
conductive material in the resin-coating layer is
insufficient to reduce the volume resistivity, and that the
adhesion between the core particle and the resin-coating
layer is unsatisfactory.
On the other hand, in order to solve the latter problem
concerning the adhesion be~ween the core particle and the
resin-coating layer, in Japanese Patent Applications Laid-
open (KORAI) Nos. 64-29857(1989) and 62-121463(1987), there
has been proposed methods of prel;min~rily surface-treating
the core particle with a coupling agent such as a Si-based
coupling agent, a Ti-based coupling agent or an Al-based
coupling agent. In the case of using the method described
in Japanese Patent Application Laid-open (KOKAI) No. 64-
29857(1989), the resin-coating layer is constituted by
thermoplastic resin polymer particles, thereby causing such
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a problem that when the resin-coated particles are mixed
with toner in a developing device, there is caused a fusion
therebetween. In the case of using the method described in
Japanese Patent Application Laid-open (KOKAI~ No. 62-
121463(1987), no additives are contained in the resin-
coating layer, thereby causing the above-mentioned problem
concerning the electrical resistivity.
Also, in order to essentially solve these problems,
there ha~e been proposed a so-called resin carrier in which
magnetic fine particles having a diameter of about 0.1 to
about 2 ~m are dispersed in an insulating resin.
Since the resin carrier has a light weight, the stress
exerted against toner when agitated therewith in a
developing device is small, so that a long life of developer
can be assured.
H~wever, since the resin carrier comprises about 30 to
about 50 % by weight of the insulating resin and the
magnetic fine particles, the saturation magnetization of the
carrier becomes low, thereby causing a so-called carrier
adhesion, i.e., such a ~nom~non that the carrier scattered
from the magnet roll of the developing device during use,
adheres to the surface of the photosensitive conductor. As
a result, there arises a problem that voids are formed in
obtained images. Therefore, it is required to recover the
carrier from the surface of the photosensitive conductor or
replenish the carrier in the developing device.
Especially in recent years, the toner has been required
to have much smaller particle size, specifically in order to
achieve a high image quality. For this reason, it has also
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been required to correspondingly reduce a par~icle size of
the carrier itself. This results in decrease of
magnetization per one carrier particle, so that the above-
mentioned problems tend to be frequently caused.
~ n addition, the printing speed of recent copying
machines or printers becomes considerably higher as compared
to those of conventional ones. ~pecifically, in order to
increase the printing speed, it is required to increase the
developing speed. As a result, it is necessary to provide
such a carrier which can be firmly retained on the
developing sleeve even when the sleeve is rotated at a high
speed. That is, the higher magnetization of the carrier is
required.
As a result of the present inventors' earnest studies
for solving the above-mentioned proble~s, it has been found
that by treating the surface of a magnetic particle as a
core particle with a surface-treating agent having an amino
group to form a coating layer comprising surface-treating
agent having an amino group, on surface of the magnetic
particle, and reacting phenols with aldehydes in an aqueous
sol~ent containing the above-treated magnetic particles,
inorganic fine particles subjected to a pre-treatment for
imparting a lipophilic property thereto in the presence of a
basic catalyst to form an outer layer comprising inorganic
fine particles and a cured phenol resin on a surface of the
surface-treating agent layer, the produced composite
particles are useful as an electrophotographic magnetic
carrier. The presen- invention has been attained on the
basis of this finding.
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SUk~ARY OF THE I~M 3NTION:
It is an object of the present invention to provide an
electrophotographic magnetic carrier not only having a high
saturation magnetization and a freely controllable charge
amount, but also being free from falling-off or separation
of magnetic fine particles from a core particle, in case
where a granulated particle comprising the magnetic fine
particles as a core particle.
To accomplish the aim, in a first aspect of the present
invention, there is provided an electrophotographic magnetic
carrier having an average particle diameter of 10 to 300 ~m,
comprising a composite particle having a two-layered
structure, comprising (i) magnetic particle as a core
particle, (ii) a coating layer formed on the surface of the
magnetic particle, comprising surface-treating agent having
an amino group, and ~iii) an outer layer formed on the
surface of the surface-treating agent layer, comprising an
inorganic material and a cured phenol resin,
the ratio (rb/r,) of an average radius (rb) of the core
particle to a thickness (ra) of the outer layer being in the
range of 10:1 to 300:1.
In a second aspect of the present invention, there is
provided an electrophotographic magnetic carrier having an
average particle diameter of 10 to 300 ~m, comprising a
composite particle having a three-layered structure,
comprising (i) magnetic particle as a core particle, ~ii) a
coating layer ~ormed on the surface of the magnetic particle,
comprising surface-treating agent having an amino group,
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(iii) an outer layer formed on the surface of the surface-
treating agent layer, comprising an inorganic material and a
cured phenol resin, and liv) a resin-coating layer formed on
the surface of said outer layer,
the ratio (rb/ra) of an average radius (rb) of the core
particle to a thickness (ra) of the outer layer being in the
range of 10:1 to 300:1.
In a third aspect of the present invention, there is
provided a process for producing an electrophotographic
magnetic carrier, comprising the steps of:
treating magnetic particles with a surface-treating
agent containing an amino group to form a coating layer
comprising surface-treating agent having an amino group on
the surface of said magnetic particle,
reacting phenols with aldehydes in an aqueous solvent
containing the treated magnetic particles and inorganic fine
particles subjected to a prelimin~ry treatment for imparting
a lipophilic property thereto in the presence of a basic
catalyst, to form an outer layer comprising said inorganic
fine particles and the cured phenol resin on a surface of
the coating layer comprising surface-treating agent having
an amino group.
BRIEF DESCRIPTION OF D ~ WINGS:
Fig. 1 is a scanning electron microscope photograph (x
5,000) showing a cross-sectional particle structure of a Mn-
zn ferrite particle used as a core particle in an Example 1
o~ the present inventioni
Fig. 2 is a sc~nn;~g electron microscope photograph (x
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1,200) showing a particle structure of a spherical composite
particle obtained according to the Example 1 of the present
invention; and
Fig. 3 is a scanning electron microscope photograph (x
5,000) showing a cross-sectional particle structure of the
spherical composite particle obtained according to the
Example 1 of the present invention.
DETATT.~ DESCRIPTION OF THE IN~n~NTION:
The present invention is explained in detail below.
First, the electrophotographic magnetic carrier
according to the present invention is described.
The composite particles according to the present
invention ha~e an average particle diameter of usually 10 to
300 ~m, preferably 10 to 200 ~m. Especially, when it is
intended to obtain an image having a high quality, the
average particle diameter of the composite particles is
preferably 20 to 200 ~m, more preferably 30 to 100 ~m. When
the average particle diameter of the composite particles is
less than 10 ~m, the carrier adhesion to a photosensitive
conductor tends to be caused. On the other hand, when the
average particle diameter of the composite particles is more
than 300 ~m, it becomes difficult to obtain a clear image.
The composite particles according to the present
invention may be of a granular shape, a spherical shape or
the like. Among them, the composite particles having a
spherical shape are preferred.
The composite particle according to the present
invention has a two-layered structure on the surface of the
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core particle, and comprises a magnetic particle as a core
particle, a coating layer cor~prising surface-treating agent t
having an amino group (hereinafter referred to simply as
~surface-treating agent layer~) and formed on the surface of
the magnetic particle, and an outer layer comprising
inorganic fine particies and a cured phenol resin and formed
on the surface of the surface-treating agent layer. The
ratio (rb/r~) of an average- radius (rb) of the core particle
to a thickness (ra) of the outer layer is usually in the
range of 10:1 to 300:1, preferab~y 20:1 to 200:1.
Incidentally, the thickness of the surface-treating
agent layer is extremely smaller as compared to the average
radius of the core particle and the thic~ness of the outer
layer, so that the above-mentioned ratio (rb/ra~ is not
influenced ~y the thickness of the surface-treating agent
layer. That is, the amount of the surface-treating agent
layer is preferably 0.05 to 1.0 ~ by weight based on the
weight of the core particle.
In the composite particles according to the present
invention, the content of the inorganic fine particles in
the outer ~ayer is preferably 80 to 99 % by weight based on
the weight of the outer layer and the content of the cured
phenol resin is preferably the h~l~nce.
In a further preferred embodiment of the present
invention, the composite particle have a three-layered
structure on the surface of the core particle, and comprises
the magnetic part}cle as a core particle, the surface-
t_eating agent layer ~ormed on the surface of the magnetic
particie, and the outer layer comprising inorganic fine
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11
particles and a cured phenol resin and formed on the surface
of the surface-treating agent layer, and a resin-coating
layer formed on the surface of the outer layer.
As the resins for the resin-coating layer, there may be
used any known resins. Examples of the resins may include
epoxy-based resins, silicone-based resins, polyester resins,
fluorocarbon-based resins, styrene-based resins, phenol-
based resins, silicon-based resins, melamine-based resins,
polyamide resins or the like.
The amount of the resin-coating layer is usually 0.05
to 10 % by weight, preferably O.l to 10 ~ by weight, more
preferably 0.2 to 5 ~ by weight based on the weight of the
composite particles to be coated, i.e., such composite
particles before forming the resin-coating layer thereon.
When the amount of the resin-coating layer is less than
0.05 ~ by weight, insufficient and non-uniform coating layer
m~y be formed, so that it may become difficult to obtain
additional improv~l-ellts or effects, for example, an effect
of freely controlling a charge amount thereof. On the other
hand, when the amount of the resin-coating layer is more
than 10 % by weight, the electrical resistivity of the
resultant composite particles may become too high, thereby
causing such a problem that the obtained image may has a
deteriorated quality.
The true specific gravity of the composite particles
according to the present invention is usually 3 to 7,
preferably 4.5 to 5.5.
The composite particles according to the present
invention may have a saturation magnetization of usually not
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~2
less than 50 emu/g, preferably not less than 60 emu/g.
The fluidity of the composite particles according to - ~
t~e present invention is usually not more than 100 seconds,
preferably not more than 80 seconds.
The percentage of change in charge amount of the
composite particles according to the present invention is
such that there exists substantially no difference in the
charge amount between before and after the particles are
subjected to a charge durability test.
As the magnetic particle used as a core particle in the
present invention, there may be exemplified magnetic
particles such as iron powder (a mechanically crushed iron
powder, an electrolytic iron powder, a reduced iron powder,
a heat-treated iron powder, a sintered iron powder or the
like); metal oxides such as ferrite particles ~Mn ferrite
p~rticles, Li-Mn ferrite particles, Ni-Zn ferrite particles,
Mn-Zn ferrite particles, Cu-Zn ferrite particles or the
like), magnetite particles, maghemite particles or the like;
alloys or mixtures of these metals or metal oxides and other
metals such as zinc or aluminum; mixtures of these metals or
metal oxides and other metal oxides such as non-magnetic
iron oxide; or mixtures thereof.
Among them, preferred magnetic particles are ferrite,
maghemite, magnetite or the like.
The average particle diameter of the magnetic particle
as a core particle is 9.98 to 270 ~m, pre~erably 10 to 200
~m, more preferably 20 ~o 200 ~m.
As the surface-treating agents having an amino group,
there may be used amino-cont~; n; ng silane-based coupling
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agents, ~mino-containing titanate-based coupling agents,
amino-containing al~min-~m-based coupling agents, amino- -
containing silicone oils, amino-cont~;n;ng surfactants or
the like.
Among these s~rface-treating agents, from the viewpoint
of adhesion to the core particlés, the amino-cont~;n;ng
silane-based coupling agents are preferred.
As the amino-cont~;n;ng silane-based coupling agents,
there may be exemplified ~-aminopropyltriethoxy silane, N-~-
(aminoehtyl)-y-aminopropyltrimethoxy silane, N-~-
~aminoehtyl)-y-aminopropylmethyldimethoxy silane, N-phenyl-y-
aminopropyltrimethoxy silane or the like.
As the inorganic fine particles usable in the present
invention, there may be exemplified iron oxides such as
hematite, maghemite or magnetite; iron oxide hydroxides such
as goethitei alumina; titanium oxide; zinc oxide; calcium
carbonate; talc; silica; silicon dioxide; or the like.
~ he volume resistivity or chargeability of the
composite particles according to the present invention may
be controlled by selectively using the inorganic fine
particles. More specifically, in the case where the
positive chargeability is to be increased, alumina particles
may be used as the inorganic fine particles. Conversely, in
the case where the negative chargeability is to be increased,
silica particles may be selectively used as the inorganic
fine particles. In addition, in the case where the
electrical resistivity is to be increased, hematite
particles may be used as the inorganic fine particles.
Conversely, in the case where the electrical resistivity is
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14
to be decreased, magnetite particles may be selectively used
as the inorganic fine particles. Further, for the purpose
of preventing the reduction of the saturation magnetization
of the resultant co~posite particles, the magnetic iron
oxides such as magnetite or maghemite are preferably u~ed as
the inorganic fine particles. Incidentally, if required,
any two or more kinds of these inorganic fine particles may
be used in combination.
The average particle diameter of the inorganic fine
particles is usually 0.02 to 10 ~m-. In view of the
dispersibility in an aqueous solvent and the strength of the
composite particles produced, it is preferred that the
average particle diameter of the inorganic fine particles is
0.05 to 5 ~m. The inorganic fine particles may be of any
shape such as a granular shape, a spherical shape, a needle-
like shape or the like.
In the present invention, it is required that the
inorganic fine particles are prel;~;n~rily subjected to a
treatment for imparting a lipophilic property thereto.
As the method of conducting such a treatment for
imparting a lipophilic property to the inorganic fine
particles, there may be exemplified a method of treating the
inorganic fine particles with a coupling agent such as a
silane-based coupling agent, a titanium-based coupling agent
or an aluminum-based coupling agent; a method of dispersing
the inorganic fine particles in an aqueous solvent
cont~;ning a surfactant to cause the surfactant to be
adsorbed on the surfaces of the particlesi or the like.
As the surfactants, there may be used commercially
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available surfactants. The preferred surfactants are those
having functional groups capable of bonding with a hydroxyl
~roup existing in the inorganic fine particles or on the
surfaces thereof. With respect to ionicity, cationic or
anionic surfactants are preferred.
Although the aim of the present invention can be
accomplished by using any of the above-mentioned treating
methods, in view of adhesion to the phenol resins, it is
preferred that the inorganic fine particles be treated with
such silane-based coupling agents having an amino group or
an epoxy group.
As the phenols used in the present invention, there may
be exemplified compo~nds having a phenolic hydroxyl group,
for example, phenol; alkyl phenols such as m-cresol, p-tert-
butyl phenol, o-propyl phenol, resorcinol or bisphenol A;
halogenated phenols having chlorine atoms or bromine atoms
substituted for a part or whole of hydrogen atoms bonded to
a benzene ring or alkyl substituents of the phenolsi or the
like. Among these phenols, phenol is most preferred. In the
case where compounds other than phenol are used as the
phenols, it may be difficult to form particles, or even if
particles are formed, the particles may be of an irregular
shape. Therefore, in view of the shape of particles
produced, phenol is most pre~erred.
As the aldehydes used in the present invention, there
may be exemplified formaldehyde in the form of any of
fonmalin or paraformaldehyde, furfural or the like. Among
these aldehydes, formaldehyde is preferred.
Next, the process for producing the composite particles
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16
according to the present i~vention, is explained below.
First, in the process according to the present
invention, it is necessary to treat the magnetic particle as
a core particle with a surface-treating agent.
As the method of treating the magnetic particles with
these surface-treating agents having an amino group, there
may be used any ordinary methods, for example, a method of
immersing the magnetic particles in a solution prepared by
dissolving the surface-treating agent having an amino group
in water or a solvent, ~ollowed by filtering and drying; a
method of spraying an aqueous or solvent-~ased solution of
the surface-treating agent on the magnetic particles while
stirring the particles, followed by drying; or the like.
Next, the reaction of phenols with aldehydes in an
aqueous solvent con~A;n;ng the above-treated magnetic
particles, inorganic fine particles subjected to a pre-
treatment for imparting a lipophilic property thereto is
conducted in the presence of a basic catalyst to form an
outer layer comprising inorganic fine particles and a cured
phenol resin on a surface of the surface-treating agent
layer
The molar ratio of the aldehydes to the phenols is
preferably 1:~ to 4:1, more preferably 1.2:1 to 3:1. When
the molar ratio of the aldehydes to the phenols is less than
1:1, it may become diffic~lt to form particles, or even if
particles are formed, it i~ dif~icult to cure the resin, so
that obtained particles tend to have a low mechanical
strength. On the other hand, when the molar ratio of the
aldehydes to the phenols is more than 4:1, there is a
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17
tendency that the amount of unreacted aldehydes remaining in
the aqueous solvent is increased.
As the basic catalyst, there may be exemplified basic
catalysts used for ordinary production of resorcinol resins.
Examples of these basic catalysts may include ~mmon; ~ water,
hexamethylene tetramine, alkyl ~m; nes such as dimethyl amine,
diethyl triamine or polyethylene imine, or the like.
The molar ratio of the basic catalyst to the phenols is
preferably 0.02:1 to 0.3:1. When the molar ratio of the
basic catalyst to the phenols is less than 0.02:1, the resin-
may not is sufficiently cured, resulting in unsatisfactory
granulation of particles. On the other hand, when the molar
ratio of the basic catalyst to the phenols is more than
0.3:1, the structure of the phenol resin may be adversely
affected, also resulting in deteriorated granulation of
particles, so that it becomes difficult to obtain aimed
composite particles.
When the phenols and the aldehydes are reacted with
each other in the presence of the basic catalyst, the amount
of the inorganic fine particles being present in the
reaction system is 75 to 99 % by weight, preferably 78 to
99 % by weight based on the total weight of the phenols and
the aldehydes. Further, in ~iew of the ~ch~n;cal strength
of the outer layer formed, the amount of the inorganic fine
particles is more preferably 80 to 99 ~ by weight based on
the total weight of the phenols and the aldehydes.
In accordance with the present invention, the reaction
between the phenols and the aldehydes is conducted in the
aqueous solvent. In this case, the amount of the aqueous
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18
solvent charged may be controlled such that the solid
concentration, e.g., carrier concentration, in the aqueous
solvent is preferably 30 to 95 % by weight, more preferably
40 to 80 % by weight.
The reaction between the phenols and the aldehydes may
be conducted by gradually heating a mixture of these
compounds up to a reaction temperature of 70 to 90~C,
preferably 83 to 87~C at a temperature rise rate of 0.5 to
1.5~C/minute, preferably 0.8 to 1.2~C/minute while stirring
and then reacting the resultant mixture at that temperature
for 60 to 150 minutes to cause the curing of the phenol
resin.
After the curing of the phenol resin, the reaction
mixture is cooled to not more than 40~C, thereby obtA;n;n~ a
water dispersion containing composite particles. The
obtained composite particles have a two-layered structure on
the surface of the core particle and comprise magnetic
particle as a core particle, the surface-treating agent
layer and formed on surface of the magnetic particle, and an
outer layer composed of inorganic fine particles and cured
phenol resin and formed on the surface of the surface-
treating agent layer.
Next, the o~tained water dispersion was subjected to
filtering, centrifugal separation and solid-liquid
separation according to ordinary methods. The separated
solid component is washed with water and then dried, thereby
obtaining the aimed composite particles.
Meanwhile, if required, a resin-coating layer may be
further formed on surface of the thus-obtained composite
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19
particle in order to improve the durability thereof and
control the charge amount thereof.
The resin-coating layer may be formed by any known
methods. For example, as the method of forming the resin-
coating layer, there may be used a method of dry-mixing the
composite particles and the resin together using a Henschel
mixer, a high-speed mixer or the like; a method of immersing
the composite particles in a resin-cont~;n;ng solvent; a
method of spraying the resin on the composite particles
using a spray drier; or the like.
In addition, as other methods for forming the resin-
coating layer, there may be exemplified a method of coating
the surfaces of the two-layered composite particles with a
melamine resin by reacting mel~m~ n~ and aldehydes in an
aqueous solvent cont~;ning the two-layered composite
particles to be treated; a method of coating the surfaces of
the two-layered composite particles with an acrylonitrile-
based polymer by polymerizing a mixture of acrylonitrile and
the other vinyl-based monomer in an aqueous sol~ent
cont~;n;ng the two-layered composite particles to be
treated; a method of coating the surfaces of the two-layered
composite particles with a polyamide resin by anionic
polymerization of lactams in an aqueous solvent cont~;ni~
the two-layered composite particles to be treated; or the
like.
The most important feature of the present invention
lies in that by forming the surface-treating agent layer on
the surface of the magnetic particle as a core particle, it
becomes possible to form the outer layer comprising
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inorganic fine particles and cured phenol resin on the
surface of the coated particle.
The reason why the outer layer can be suitably formed
on the magnetic particle by forming the surface-treating
agent layer on the surface of the magnetic particle as a
core particle, is considered as follows.
That is, it is considered that the amino group
contained in the surface-treating agent which constitutes an
intermediate coating layer, acts as a starting point for the
reaction for the production of the phenol resin, i.e.,
exhibits a so-called anchor effect for the phenol resin.
Consequently, it is considered that the phenol resin is
cured over the surface of the surface-treating agent layer
while ~ncorporating the inorganic fine particles therein.
On the other hand, in the case where the surface-treating
agent which constitutes an intermediate coating layer, has
no amino group, the mixture of the phenol resin and the
inorganic fine particles are granulated into small particles
independent of the magnetic particle as a core particle, as
described in Comparative Example 3 hereinafter. Therefore,
it is considered that the existence of the surface-treating
agent layer is effective to form the outer layer.
By the formation of the outer layer comprising the
inorganic fine particles and the c~red phenol resin, it is
possible to control various properties such as volume
resistivity, chargeability or magnetic properties of the
resultant composite particles according to a kind of
developing system used.
In addition, since irregularities on the surfaces of
~ CA 02242058 1998-06-30
the core particle can be buried and eliminated by forming
the outer layer comprlsing the inorganic fine particles and
the cured phenol resin thereover, the sphericity of the
obtained co~posite particles can be ~nh~nced. The ~nh~nced
sphericity of the composite particles results in not only
improvement in fluidity thereof and increase in charging
speed of toner, but also preventing the spent phenom~non
that the toner is deposited in the concave portions thereof.
Further, the composite particles according to the
present invention can exhibit an excellent adhesion between
the core particle and the outer layer. Therefore, the outer
layer can be prevented from being peeled-off or separated
from the core particle during use.
Since the outer layer comprises the cured phenol resin
in which the inorganic fine particles dispersed, it becomes
possible to lessen the damage to toner and to prevent the
spent phenomenon.
In addition, in the case where a resin-coating layer is
further formed on the surface of the outer layer comprising
the inorganic fine particles and phenol resin, it becomes
possible to obtain additional improvements or effects, for
example, it is possible to freely control the charge amount
of the composite particles. Further, the resin-coating
layer can function as a protecting layer of the outer layer,
resulting in increasing the durability of the resultant
composite particles.
The composite particles according to the present
invention can ha~e a high saturation magnetization and a
freely controllable charge amount, and is free from falling-
CA 02242058 1998-06-30
off or separation of magnetic fine particles from the core
particle. Accordingly, the composite particles according to
the present invention are useful as an electrophotographic
magnetlc carrler.
EX~PL~S:
The present invention will now be described in more
detail with reference to the following examples, but the
present invention is not restricted to those examples and
various modifications are possible within the scope of the
nventlon .
In the following Examples and Comparative Examples, the
averaae particle di~m~.ter of particles was meas~red by a
laser diffraction-type granulometer (manufactured by HORIBA
SEISAKUSHO CO., LTD.~. In addition, the shape of particles
was observed ~y a sc~3nn;ng electron microscope S-800
(manufactured ~v HITACHI LIMITED).
The saturation mann~tizatio~ was measured at an
external magnetic field of 10 kOe bY a sample vibration-type
magnetometer VSM-3S-15 (manufactured by TOEI KOGYO CO.,
LTD.).
The true s~ecific qravitY was measured by a multi-
volume densitometer (manufactured ~y MICROMELITIX CO., LTD.).
The volume resistivit~ was measured by a high
resistance meter 4329A (manufactured by YOKOGAWA HEWLE~
PACK~R~ CO., LTD.).
The fluiditY was expressed by a flow rate calculated bY
dividing the weight (50 g) of composite particles by a drop
time (second) thereof, which drop time was measured by
CA 02242058 1998-06-30
23
dropping the composite particles filled in a glass funnel
(opening: 75~; heiqht: 75 mm; inner diameter of conical
section: 6~; length of straight pipe section: 30 mm) by
applying a predetermined amount of ~ibration to the funnel.
The r~ ]~ (rb) of core Darticles of the composite
particles and the thickness (r~) of the outer l~yer
comprising inorganic fine particles and cured phenol resin
were obtA;ne~ by the following method.
The scanning electron microscope photograph of cross-
section of the composite particles was observed to measure
an average thickness (r~) of the outer layer contA;ning
inorganic fine particles. The radius (rb) of the core
particles was calculated from the thickness (r~) and a
previously obt~ine~ average particle diameter of the
composite particles. The ratio (rb/r~) was obtained from
these values (ra) and (rb).
The ~lr~hility test of the composite particles having a
resin-coating layer was conducted in the following manner.
That is, 50 g of the composite particles were filled in
a 100 cc glass sampling bottle, which was then capped and
shaken for 10 hours by using a paint conditioner
(manufactured by RED DEVIL CO., LT~.). The charge amounts
of respec~ive samples of the composite particles were
measured before and after being shaken.
The ~h~rqe ~nl]nt was obtained as follows. That is,
using 200 mg of a mixture of 95 parts by weight of the
composite particles and 5 parts by weight of toner (CLC-200
sLAcK produced by CANON CO. LTD.), a value A (~C) was
measured ~y a blow-off charge measuring apparatus MODE~ Ts
CA 02242058 1998-06-30
24
200 (manufactured by TOSHIBA CHE~ICAL CO., LTD.). The
charge amount was calculated as a value per one gram of the-
composite particles according to the following formula:
[A x 1/(0.2 x 0.05) (~C/g)]
As recognized from the scanning electron microscope
photograph (x 5,000) of Fig. 1 showing a cross-sectional
structure of particle, the Mn-Zn ferrite particles used as
core particles had a large number of irregularities on the
surface thereof.
Exam~le 1
One kilogram of Mn-Zn ferrite particles having an
average particle diameter of 60 ~m were charged into a
Henschel mixer and intimately agltated. Thereafter, 1.0 g
of a silane-based coupling agent containing an amino group
~KBM-602 produced by SHIN-ETSU KA~AKU CO., LTD.) was added
to the ferrite particles, and the mixture was heated to
about 100~C and intimately mixed and stirred at that
temperature for 30 minutes, thereby obtaining core particles
coated with the coupling agent.
Similarly, one kilogram of spherical magnetite
particles having an average particle diameter of 0.23 ~m
were charged into a Henschel mixer and intimately stirred.
Thereafter, 10 g of a silane-based coupling agent (KBM-403
produced by SHIN-ETSU KAGAKU ~O., LTD.) was added to the
magnetite particles, and the mixture was treated in the same
manner as descri~ed above, thereby obt~;n;~g inorganic fine
particles coated with the coupling agent.
Separately, 5 g of phenol, 7 g of 37 % formalin, 400 g
CA 02242058 1998-06-30
of the above surface-treated core particles, 20 g of the
inorganic fine particles subjected to the above treatment
for imparting a lipophilic pro~erty thereto, 5 g of 25 %
ammonia water and 418 g of water were charged into an one-
liter four-neck f lask. The ~ixture was heated to 85~C for
60 minutes while stirring and reacted at that temperature
for 120 minutes to cure a resin component therein, thereby
forming a phenol resin layer cont~in;ng the inorganic fine
particles, on the surface of the core particles.
Next, after the content of the flask was cooled to 30~C,
0.5 liter of water was added thereto. Thereafter, the
supernatant was removed, and the obtained precipitate was
washed with water and then dried ~y blowing air.
The resultant dry product was further dried under
reduced pressure (not more than 5 mmHg) at a temperature of
150 ~o 180~C to obtain composite particles.
The average particle diameter of the thus obt~ine~
composite particles was 63 ~m. As recognized from the
scanning electron microscope photograph (x 1,200~ of Fig. 2,
the obtained composite particles exhibited a high sphericity.
Further, as recognized from the scAnnin~ electron microscope
photograph (x 5,000) of Fig. 3 showing a cross-sectional
structure of the composite particle, the irregularities on
the surface of the composite particle were buried and
eliminated, so that the composite particle had a smooth
suLrface.
It was also determined that the obtained composite
particles exnibited excellent properties required for an
electrophotographic developing carrier.
CA 02242058 1998-06-30
Specifically, the obtained comp~site particles had a
specific gravity of 5.02, a fluidity of 25 seconds and a
volume resistivity of 7 x 107 Qcm. In addition, it was
determined that the total content of the magnetic particle~
(amount of a sum of Mn-Zn ferrite particles as core
particles and spherical magnetite particles as magnetic
inorganic fine particles based the total weight of the
composite particles) was 98.9 % by weight, and the content
of the inorganic fine particles in the outer layer was 81 %
by weight based on the weight of the outer layer. With
respect to magnetic properties of the obtained composite
particles, the saturation magnetization thereof was 66.7
emu/g; the radius (r~) of the core particles was ~0 ~m; the
thickness (ra) of the outer layer was 3 ~m; and, therefore,
the ratio (rb/r~) was 10. The amount of the surface-treating
agent layer was 0.1 % by weight based on the weight of the
core particle.
<Production of composite particles>
Exam~les ~ to 5:
The same procedure as defined in Example 1 was
conducted except that kind of the core particles, kind and
amount of the surface-treating agent used for the core
particles, kind and amount of the inorganic fine particles,
kind and amount of the treating agent for Lmparting a
lipophilic property to the inorganic fine particles, amount
of phenol, amount of formalin, amount of ~mmonia water as a
basic catalyst and ar,ount of water were varied, thereby
producing composite particles. The production conditions
"-- - CA 02242058 1998-06-30
"~ ~
are shown in Table 1 and various properties of the obtained
composite particles are shown in Table 2.
Com~arative Exam~le 1:
The same procedure as defined in Example 1 was
conducted except that the core particles were subjected to
no surface-treatment, the inorganic fine particles were not
subjected to the treatment for imparting a lipophilic
property thereto, and amount of phenol, amo~nt of formalin,
amount of water and amount of ammonia water as a basic
catalyst were varied as shown in Table 1.
It was determined that the obt~ine~ product was a
mixture of the core particles and separately granulated
small particles composed of the inorganic fine particles and
a phenol resin.
Comparative ~amDle 2:
The same procedure as defined in Example 1 was
conducted except that the Mn-Zn ferrite core particles were
subjected to no surface-treatment, and kind and amount of
the inorganic fine particles, kind and amount of the
treating agent for imparting a lipophilic property to the
inorganic fine particles, amount of phenol, amount of
formalin, amount of ammonia water as a basic catalyst and
amount of water were varied as shown in Table 1.
It was determined that the obtained product was a
mixture of the core particles and separately granulated
small particles composed of the inorganic fine particles and
a phenol resin.
CA 02242058 1998-06-30
28
Com~arative Ex~m~le 3:
The same procedure as defined in Example 1 was
conducted except that the Mn-Zn ferrite core particles were
treated with a silane-based coupling agent cont~; ni ng no-
amino group, and kind and amount of the inorganic fine
particles, kind and amount of the treating agent for
imparting a lipophilic property to the inorganic fine
particles, amount of phenol, amount of formalin, amount of
ammonia water as a ba~ic catalyst and amount of water were
varied as shown in Table 1.
It was determined that the obtained product was a
mixture of the core particles and separately granulated
small particles composed of the inorganic fine particles and
a phenol resin.
CA 02242058 1998-06-30
29
~able 1
Examples and Production conditions of composite particles
Comparative Core particles
Examples Kind Average Amount (g)
particle
diameter (2rb)
(~)
Example 2 Ni-Zn ferrite 70 400
Example 3 Mn-Zn ferrite 100 400
Example 4 Magnetite 50 400
Example 5 Cu-Zn ferrite 60 ~00
Comparative Mn-Zn ferrite 80 400
Example 1
Comparative Mn-Zn ferrite 80 400
Example 2
Comparative Nn-Zn ferrite 80 400
Example 3
CA 02242058 1998-06-30
Table 1 (continued)
Production conditions of composite particles
Examples and Core particles
Comparative Surface-treating agent
Examples Kind Amount applied
(~
Example 2Silane-based coupling agent 0.10
(KBM-602 produced by SHTN-
ETSU KAGAKU Co., LTD.)
Example 3Silane-based coupling agent 0.15
~K~M-602 produced by SHrN-
ETSU KAGAKU CO., LTD.)
Example 4Silane-based coupling agent 0.10
(KBM-902 produced by SHIN-
ETSU KAGAKU CO., LTD.)
Example 5Silane-based coupling agent 0.15
(KBM-602 produced by SHIN-
ETSU KAGAKU CO., LTD.)
Comparative - O
Example 1
Comparative - O
Example 2
Comparative Silane-based coupling agent 0.10
Example 3 (KBM-403 produced ~y SHIN-
ETSU KAGAKU CO., LTD.)
~ f
CA 02242058 l998-06-30
31
Table 1 (continue~)
Proauction condit7ons of composite particles
Conditions for formation of outer layer
Examples Inorganic fine particles
and Kind Amount Treating agent for imparting
Comparative (particle (g) lipophilic prope-ty
Examples diameter: Kind Amount
~m) treate
d ~%)
Example 2 Octahedral 10 Silane-based coupling 1.0
magnetite agent (KBM-603
(O.30 ~m~ produced by SHIN-ETSU
KAGAKU CO., LTD.)
Example 3 Granular 6 Silane-based coupling 1.5
hematite agent (KBM-402
(0.12 ~m) produced by SHIN-ETSU
KAGAKN CO., LTD.)
Example 4 Gr~n~ r 2 Silane-based coupling 2.0
titanium agent (KB~-403
oxide produced by SHIN-ETSU
(0.20 ~m) KAGAKU CO., LTD.~
Example 5 Spherical 10 Silane-based coupling 1.5
magnetite agent (KBM-403
(O.2 ~m) produced by SHrN-ETSU
Plate-like 5KAGAKU CO., LTD.)
alumina
(0.5 ~m)
Comparative Spherical 10 - O
Example 1 m2gnetite
(0.23 ~m3
Comparative Spherical 10 Silane-based coupling 2.0
Example 2 magnetite agent (KBM-403
(O.23 ~m) produced by SHIN-ETSU
KAGAKU ~0., LTD.)
Comparative Spherical 10 Silane-based coupling 0.8
Example 3 magnetite agent (KBM-403
(O.23 ~m) produced by SHIN-ETSU
KAGAKU ~O , LTD.)
CA 02242058 1998-06-30
Table 1 (continued)
Examples Production conditions of composite particles
and Cond: tions for forming outer la~er
Comparative Amount Amount Basic catalyst Amount
Examples of of 37 % Kind Amount of water
phenol formalin ~g) (g)
(g) (g)
Example 2 3 4 Ammonia 3 410
water
Example 3 1.5 2 Ammonia 1.5 404
water
Example 4 1 1.5 Ammonia 1 402
water
Example 5 3 4 Ammonia 3 420
water
Comparative 3 4 Ammonia 3 410
Example 1 water
Comparative 3 4 Ammonia 3 410
Example 2 water
Comparative 3 4 Ammonia 3 410
Example 3 water
Table 2
Examples Prop~rties of composite particles
and Shape Average Specific Fluidity
Comparative particle gravity (sec)
Examples diameter
(~m)
Examp e ~ Sp~er ca:72 ._'
Examp e Spler_ca 102
Examp_e ~ Spler:.ca_ 51 ..
Examp e Sp~er:ca. 63
comparative Sm~l_ par-icles were formed ndependent of
Example 1 core particles
Comparative Small particles were formed independent of
Example 2 core particles
Compar~tive Small particles were ~ormed independent of
Example 3 core particles
CA 02242058 1998-06-30
Table 2 (continued)
Examples Properties of composite particles
and Volume Total content Content of
Comparative resistivity of magnetic inorganic fine
Examples (Qcm) particles particles in outer
. %) layer (based on
total weight of
outer layer
(wt. ~)
Example 2 3 x 10799.5 82.9
Example 3 7 x 10~98.2 81.8
Example 4 2 x 10~99 4 82.8
Example 5 5 x 108g9.0 88.7
Comparative Small part_cles were formed independent of
Example 1 core particles
Comparative Small particles were formed independent of
Example 2 core particles
Comparative Small particles were formed independent of
Example 3 core particles
Table 2 ~cont;n~
Examples Properties of co~posite part_cles
and Saturation Radius Thickness rb/r~
Comparative magnetiza- (rb) of (ra) of
Examples tion ~score outer
(emu/g)particles layer
(~) '~,)
Examp:e ~ n7. 3 .. ~ 23
Examp e ~:. ., 71
Examp e ~ .3 3
Examp_e ~ .7 ~4
Comparative Small particles were formed independent of
Example 1 core particles
Comparative Small particles were formed independent of
Example 2 core particles
Comparative Small particles were formed independent of
Example 3 core particles
CA 022420S8 1998-06-30
34
<Formation of resin-coating layer>
ExamDle 6: --
One kilogram of the composite particles ob~;ne~ inExample 1 and 5 g (as a solid content) of a silicone resin
(KR-251 produced by SHIN-ETSU KAGAKU CO., LTD.) were charged
into a Henschel mixer under a nitrogen stream. The mixture
was heated to 120~C while agitating, and further agitated at
that temperature for one hour, thereby forming a resin-
coating layer composed of the silicone resin on the surfaces
of the composite particles.
Various properties of the obtained composite particles
having the resin-coating layer are shown in Table 3. It was
determined that the surfaces of the particles were uniformly
coated with the silicone resin.
Examples 7 to 10:
The same procedure as defined in Example 6 was
conducted except that kind of the composite particles used
and kind and amount of the coating resin were varied,
thereby producing composite particles having a resin-coating
layer. The production conditions and various properties of
the obtained composite particles are shown in Table 3.
Com~arative ~x~mple 4:
The same procedure as defined in Example 6 was
conducted except that the ~n-Zn ferrite core particles
obtained in Example 1 were used as particles to be resin-
coated, instead of the composite particles, and the resin-
coating layer was formed directly on the surfaces of the
CA 02242058 1998-06-30
core particles.
Various properties of the obtained resin-coated Mn-Zn
ferrite particles are shown in Table 3.
Table 3
Examples and Conditions for forming resin-coating layer
Comparative Particles to be resin-coated
Examples Kind Weight tkg)
Exar~le 6Co~posite particles obta; neA in 1.0
Example 1
Example 7Composite particles obtA;neA in 1.0
Example 1
Example 8Composite particles obt~;ne~ in 1.0
~xample 2
Example 9Composite particles obtained in 1.0
Example 3
Example 10Composite particles obtained in 1.O
Example 3
Comparative Mn-Zn ferrite particles used as 1.0
Example 4core particles in Example 1
CA 022420~8 1998-06-30
36
Table 3 (continued)
Examples and Conditions for forming resin-coating layer
ComparativeCoating resin
Exa~ples Kind Amount
treated (%)
Example 6Silicone resin ~KR-251 produced0.5
~y SH~N-ETSU KAGAKU CO., LT~.)
Example 7Polyester resin (FC-022 1.0
produced by MITSUBISHI RAYON
CO., LTD.)
Example 8Epoxy resin (EPICRON 850 0.8
produced by DAI-NIPPON INK CO.,
LTD.)
Example 9Styrene-based resin ~BR-52 1.5
produced by MITsusIsHI RAYON
CO., LTD.)
Example 10Fluorocar~on resin (KF POLYMER 0.7
produced by KUREHA KAGAKU KOGYO
CO., LTD.)
Co~parative Silicone resin (KR-251 produced 0.5
Example 4by SHIN-ETSU KAGAKU CO., LTD.)
Table 3 ~continued)
Properties of composite particles having resin-
coating layer
ExamplesAmount Volume Saturation Durability
of te-t
andcoating resistivity magneti- Charge Charge
Comparative resin ( ~ ) zationamount amount
Examples (wt.%~ (emu/g)before after
test test
(llC/g) (,UC/g)
Example 6 0.4 7 X108 66.4 -25 -23
Example 7 0.9 5 x10~ 65.7 -35 -35
Exa~le 8 0.8 8 xlol1 67.1 -30 -31
Example 9 1. 4 4 X1015 62 . O-~5 -42
Example 10 0.5 2 x10l0 62.3 -42 -42
Comparative 0.4 8 xlC9 66.8 -27 -5
Example 4
